Millions of people are affected by sleep apnea, a condition in which a person's breathing is interrupted, often repeatedly, during their sleep due to the person's airway becoming blocked. Sleep apnea can cause chocking spells, fatigue, mood swings, and more serious conditions. Fortunately, sleep apnea is a treatable condition.
Breathing is controlled by a pair of nerves called the “phrenic nerves” which are located in the neck, at the base of the brain, and extend down to the diaphragm. The phrenic nerves carry the stimuli from the brain to the diaphragm, the primary muscle used in breathing. When a person breathes in, the diaphragm moves down and air moves into the lungs. This is called inspiration. When the person breathes out, air moves out of the lungs. This is called expiration. When no stimuli are present in the phrenic nerves, the diaphragm does not contract to create more air space. As a result, the person's breathing is interrupted.
Implantable stimulation devices have been proposed to treat people who suffer from sleep apnea. These devices send stimulation pulses to the phrenic nerves to control the diaphragm and thus the person's breathing. Timing of such stimulation pulses is critical as any incorrect or untimely stimulation pulses may alarm/surprise the person. Moreover, closely spaced respiration may not be effective in air movement. Specifically, untimely and/or incorrect stimulation signals can wake up the sleeping person, thus compromising the person's already unstable sleeping session due to sleep apnea.